Field of the Invention
The present invention relates to an air/oil-cooled internal combustion engine whose temperature is detected with oil having cooled a cylinder head.
Description of Related Art
For example, Patent Documents Japanese Patent Application Publication No. 2013-072353 (FIGS. 3 to 11) and Japanese Patent Application Publication No. 2012-215172 (FIGS. 2 to 16) describe an air/oil-cooled internal combustion engine including: cooling fins which are provided on the circumferences of a cylinder block and a cylinder head; and a cooling passage which is provided in a combustion chamber upper wall covering a combustion chamber of the cylinder head and is used for cooling the combustion chamber upper wall with lubrication oil.
In the internal combustion engine described in Japanese Patent Application Publication No. 2013-072353 and Japanese Patent Application Publication No. 2012-215172, oil having cooled the cylinder head is directly sent back to an oil pan portion after passing through a cooling passage.
Meanwhile, accurate detection of a warm-up condition of an internal combustion engine has been requested for the air intake control during the warm-up operation. However, detection of the temperature of an internal combustion engine has been heretofore carried out by collecting lubrication oil having dripped from a valve system of a cylinder head and detecting the temperature of this oil with a temperature sensor.
In view of the above existing technique, a challenge of the present invention is to provide an air/oil-cooled internal combustion engine capable of increasing accuracy in detection of the temperature of the air/oil-cooled internal combustion engine by a temperature sensor and carrying out the warm-up operation after the start-up of the air/oil-cooled internal combustion engine favorably.